Zero speed switch



June 18, 1963 o. HERMANN 3,094,595

ZERO SPEED SWITCH Filed Oct. 20, 1960 2 Sheets-Sheet 1 ad -m June 18, 1963 o. HERMANN ZERO SPEED SWITCH 2 Sheets-Sheet 2 Filed Oct. 20, 1960 INVENTOR.

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mut 74 87 nite rates This invention relates to electric switches and is particularly concerned with electric switches sensitive to rotation. In many instances, as in connection with machine tools and the like, it is desirable to determine the instant at which a rotating shaft comes to a halt. This might be desired, in connection with a machine tool such as a lathe, for example, in order to determine the instant at which gears could be safely shifted.

Zero speed switches are known but have heretofore been relatively expensive and, furthermore, are effective in only one direction of rotation. While a switch effective in only one direction of rotation is useful in many instances, it is also desirable many other times to have a switch which is sensitive to rotation in both directions. A switch of this nature could be employed in connection with a reversing, for example, drive thereby simplifying the circuitry and reducing costs.

With the foregoing in mind, a primary object of the present invention is the provision of an improved zero speed electric switch.

A still further object of this invention is the provision of a zero speed electric switch which will operate in either direction of rotation.

Still another object of this invention is the provision of a Zero speed switch which is compact and inexpensive which can readily be attached to a rotating member, such as a shaft and which will occupy a minimum amount of space and to which switch electrical connections can easily he made.

Another particular object of this invention is the provision of a zero speed switch especially adapted for use in connection with machine tools, such as lathes, which can be employed for preventing shifting of gears of the machine tool when the machine tool is operating.

These and other objects and advantages of this invention will become more apparent upon reference to the following specification taken in connection with the accompanying drawings in which:

FIGURE 1 is a diagrammatic view showing a simple lathe arrangement in which a zero speed switch according to the present invention is incorporated;

FIGURE 2 is a vertical sectional view through one form of the switch;

FIGURE 3 is a transverse sectional view indicated by line 3-3'on FIGURE 2;

FIGURE 4 is a vertical sectional view through a modilied form of the switch; 7

FIGURE 5 is a view similar to FIGURE 3 but shows another modification of the switch;

FIGURE 6 is a transverse sectional View through the switch of FIGURE 5 and indicated by line 6-6 on FIGURE 5;

FIGURE 7 is a view showing the switch of FIGURE 5 in another rotated position thereof;

FIGURE 8 is a fragmentary view of a switch like that of FIGURE 5 showing a different construction;

FIGURE 9 is a diagrammatic view showing a brake associated with the shifting means of the gear box of the lathe;

FIGURE 10 is a diagrammatic representation of a control circuit in which the switch of FIGURES 2, 3 and 4 can be embodied; and

FIGURE 11 is a diagrammatic representation of an electric control circuit for the lathe in which the switch of FIGURES 5 to 8 can be embodied.

Referring to the drawings somewhat more in detail, the lathe of FIGURE 1 comprises a bed 10, a head stock 12, a tail stock 14, and a carriage 16. The head stock 12 has a gear box therein and includes a shifting means such as the shiftable lever 18 by means of which the drive ratio of the gearing in the head stock can be changed. This will change the drive ratio between the motor driven pulley 20 and the spindle 22 of the head stock to determine the speed of rotation of the spindle thereby to ob tain the cutting speed desired at the surface of the work piece supported by the spindle.

Mounted on the input shaft 24 to which pulley 20 is attached is a zero speed switch 26 according to this invention which is connected in an electric control circuit that is effective for preventing movement of lever 18 whenever the pulley 20 and shaft 24, and therefore, the spindle 22 is rotating.

In one form of the Zero speed switch, the switch is closed when shaft 24 is not rotating and opens when shaft 24 commences to rotate and remains open until the shaft comes to a halt.

This form of the switch is illustrated in FIGURES 2 and 3. In these figures, it will be noted that the switch comprises a metal body part 28 having a groove 30 therein in which there is a pool of mercury 32.

A smaller metal part at 34 is mounted in body part 28 with an insulating ring 36 interposed therebetween. An insulating bushing or sleeve 38 extends between the axial portions of the body parts. A disc 37 attached to :body part 28 provides means for supporting the switch on the rotating member or shaft 24 while simultaneously insulating all parts of the switch from the shaft.

Each of the body parts 28 and 34 has a smooth annular surface thereon, as at 40 and 42 on which the brushes or current collectors 44 and 46 ride so that electrical connection can be made with the switch while it is rotating. The brushes are urged toward the switch body by the springs 45 and 47 which are attached to the insulating brush holder 49.

As will be seen at FIGURES 2 and 3, the pool of mercury at 32 is of such a size that it will bridge between the body parts 28 and 34 when the switch is stationary thus establishing electrical connection between the brushes 44 and 46. As soon as the switch commences to rotate, however, the pool of mercury commences to flatten out, on account of centrifugal force acting thereon, and at quite a low speed of rotation of the switch, the bridging connection between the body parts 28 and 34 will be interrupted.

The pool of mercury eventually flattens out into a thin ring of mercury inside the groove 30 and will again form a pool at the bottom of the switch that will bridge between the electrically conductive body parts of the switch, only when the shaft and switch have again come to a halt.

There are many ways in which a switch of this nature can be employed for effecting control functions that are not to be initiated until the shaft pertaining to the switch, or some part connected thereto, comes to a complete halt.

In the present case, the shifter lever 18 is attached to a shaft Sit and to prevent movement of lever 18 and shaft 50, except when the spindle drive shaft 24 is at a complete halt, there is provided hrake means 52 associated with shaft 50. This brake means is normally engaged by a spring 54 and when the brake is engaged the shaft 50 cannot be rotated. Also associated with the brake are the solenoids S, which, when energized, open the brake thereby releasing the shaft.

It will be evident that many other detaining means could be provided for the shaft, including positively engaging detaining means and that the brake arrangement illustrated is purely exemplary and is not intended in any way to limit the scope of the present invention but is intended to show, broadly, shifting means, or the like.

Still further there could be multiple elements to belocked in place, or otherwise controlled, by the zero speed switch and it will be apparent that multiple control devices, such as the detaining means described, could be controlled by being placed in circuit with the switch, if so desired.

FIGURE 10 shows a simple electrical control circuit in which the switch of FIGURES 3 and 4 and the brake of FIGURE 9 can be embodied. In this circuit, the power lines are indicated at L1 and L2. Connected therebetween is a relay R1 having a blade 6%] in circuit with the drive motor M that drives pulley 20.

A second relay R2 has normally open blades in circuit with the solenoids S of the brake.

The zero speed switch is indicated at 26.

In the circuit of FIGURE 10, if motor M is deenergized, it can be energized by closing start switch 62. As soon as the motor starts, switch 26 will open and deenergize relay R2 which will cause deenergization of solenoids S whereupon brake 52 will close and lock shifter shaft 59 in place.

Shaft 50 will remain locked by the brake until motor M is halted by actuating the stop switch 64 which will deenergize relay R1 and thus deenergize motor M.

When the motor M comes to a halt, thus halting pulley 20 and shaft 24 and switch 26, switch 26 will close thus energizing relay R2 and therethrough solenoids S to release brake 52.

It will be evident that the zero speed switchwould be equally effective in both directions of rotation and that, furthermore, since the switch embodies a pool of mercury, the characteristics of the switch, namely, the speed at which it will open, and the delay between the time the switch halts and the mercury again forms a bridging pool between the body parts of the switch, can be controlled by selecting the quantity of mercury employed in the switch, and by the size of the switch, and other variable factors, such as the shape of the cavity.

FIGURE 4, for example, shows a switch like that of FIGURE 2 except the main body part 51 is formed of parts that define a restricted opening 53 through which the mercury must flow when the switch stops. By adjusting the size of the opening 53, any desired time delay can be built into the switch.

The delay feature could be provided by other means, such as a perforated cylinder in the switch separating the two portions of the cavity, namely, the portion in which the mercury is disposed when the switch is rotating, and the portion in which the center member of the switch is located.

The switch described, is one in which the switch is closed at zero speed and is opened when rotating. My invention can be practiced, however, in a switch which is open when stationary and which closes when rotating. A switch of this nature is illustrated in FIGURES through 8.

In these figures, it will be seen that the switch comprises an outer body part 70 of electrical insulating material. This body part 76 has a cavity 72 therein in which there is a pool of mercury at 74. At the open end of the cavity, there is an electrically conductive ring 76 carrying conductive pins 78 that extend inwardly in the cavity axially at the periphery thereof.

The pins carried by rings 76 are spaced apart a peripheral distance which is somewhat greater than twice the peripheral length of the pool of mercury in the cavity.

As will be seen in FIGURE 5, there is a second electrically conductive ring 80 spaced from ring 76 by a washer 82 of electrical insulating material. Ring 80 also carried electrically conductive pins 84 which extend through ring 76 through the insulating bushings 86. Pins 84 also extend axially into cavity '72 on the periphery thereof and have the same circumferential spacing as the pins 78 and are positioned midway therebetween.

As will be seen in FIGURE 6, the pins are so spaced that the pool of mercury 74-- cannot bridge between any two adjacent pins except when the pool of mercury is flattened out by rotation of the switch. The switch of this second modification is therefore open at zero speed and closed when it is rotating.

The rings '76 and 8t) have pertaining thereto the brush elements 88 and effecting electrical connection with the switch.

The body part 70 of the switch is mounted on a disc 92 of electrical insulating material which provides means for mounting the switch on a supporting and rotating member, such as a shaft.

FIGURE 8 shows how the switch could be made by printing or plating the contact elements 81 and 83 in an insulating cup 85. Electrical contact with the contact elements could be made via the disc 87 and ring 89 on the outside of the cup.

The electrical circuit of FIGURE 11 shows how the zero speed switches of FIGURES 5 and 8 could be embodied in an electrical control circuit for the lathe and including the brake 52 of FIGURE 9.

In FIGURE 11, the motor M is connected by power lines L1 and L2 and the energization thereof is under the control of a relay R3.

The solenoids S of the brake are under the control of a relay R4 which has blades that close when the relay is deenergized for energizing the solenoids S and which blades open when the relay is energized to deenergize the solenoids S.

The zero speed switch, indicated by reference numerals 26a is in circuit with the energizing coil of relay R4. It will be evident that when the rotation of the switch is halted, the switch will open and relay R4 will be deenergized thus energizing solenoids S to release brake 56 so that shifting operations can be carried out.

When the motor is again started, switch 26a will close thus energizing relay R4 and opening its blades to. deenergize solenoids S thus permitting brake 52 to close on shaft 50 and hold it against rotation.

From the foregoing, it will be evident that the present invention provides for a simple inexpensive and compact zero speed electrical switch arrangement effective in both directions of rotation and adapted for easily being included in a machine structure and an electrical control circuit.

It will be understood that this invention is susceptible to modification in order to adapt it to different usages and conditions; and, accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope of the appended claims.

I claim:

1. An electric switch of the zero speed type comprising: a substantially cylindrical body of electrical insulating material adapted for rotation on its axis", a generally cylindrical cavity extending into said body from one side thereof concentric with said axis, means closing the cavity at the said one side of the body comprising a cover member of electricalinsulating material attached to said body, uniformly circumferentially spaced contact elements extending axially into the cavity at the periphery thereof, a body of mercury in the cavity forming a pool therein when the switch is not rotating of smaller circumferential extent than the distance between adjacent ones of said contact elements and forming an annular layer about the periphery of said cavity when the switch is rotating on said axis, said layer electrically interconnecting said elements, first and second electrically conduc tive ring members concentric with said axis caried by said body and insulated from each other, alternate of said contact elements being connected with different ones of said ring members, said contact elements being printed in said cavity, and means carried by the switch entirely 5 outside said cavity for connecting the switch to the end of a rotary member.

2. An electric switch of the zero speed type comprising: a metal body part which is arranged for rotation about its central horizontal axis, a generally cylindrical cavity extending into said metal body part from one side and concentric with said axis, said cavity terminating in an annular groove, a smaller metal part having a cylindrical shaped port-ion for fitting into the cylindrical cavity of said metal body part and closing the same, means attached to said metal body part for supporting said metal body part and smaller metal part of the switch on a rotary shaft and for electrically insulating the metal body part from the shaft, a mass of mercury in said groove forming a pool therein which makes electrical contact between a portion of said metal body part and said smaller metal part when said switch is not rotating and forming an annular layer of mercury about said groove which breaks electrical contact connections between said metal parts when said switch is rotating, and first and second electrically conductive ring members arranged to contact said metal body part and said smaller metal part respectively, said conductive ring members being electrically insulated from each other.

3. An electric switch of the zero speed type comprising: a metal body part which is arranged for rotation about its central horizontal axis, a cavity extending into said metal body part from one side and having its central axis common with said horizontal axis, said cavity terminating in an annular groove, a smaller metal part having a shaped portion for fitting into said cavity of said metal body part and closing the same, means comprising electrical insulating material aranged between said smaller metal part and said metal body part, means attached to said metal body part for supporting said metal body part and smaller metal part of the switch on a rotary shaft and for electrically insulating the metal body part from the shaft, a mass of mercury in said groove forming a pool therein which makes electrical contact between a portion of said metal body part and said smaller metal part when said switch is not rotating and forming an annular layer of mercury about said groove which breaks electrical contact connection between said metal parts when said switch is rotating, and first and second electrically conductive ring members aranged to contact said metal body part and said smaller metal part respectively, said conductive ring members being electrically insulated from each other.

References Cited in the file of this patent UNITED STATES PATENTS 973,525 Lucas Oct. 25, 1910 1,785,705 Taylor Dec. 16, 1930 1,897,851 Leach Feb. 14, 1933 2,359,042 Lambert Sept. 26, 1944 2,515,710 Holmes July 18, 1950 2,583,273 Miller Ian. 22, 1952 2,655,579 Burroughs Oct. 13, 1953 2,705,271 Erich Mar. 29, 1955 2,918,545 Von Bomhard Dec. 22, 1959 FOREIGN PATENTS 122,290 Great Britain Ian. 23, 1919 

1. AN ELECTRIC SWITCH OF THE ZERO SPEED TYPE COMPRISING: A SUBSTANTIALLY CYLINDRICAL BODY OF ELECTRICAL INSULATING MATERIAL ADAPTED FOR ROTATION ON ITS AXIS, A GENERALLY CYLINDRICAL CAVITY EXTENDING INTO SAID BODY FROM ONE SIDE THEREOF CONCENTRIC WITH SAID AXIS, MEANS CLOSING THE CAVITY AT THE SAID ONE SIDE OF THE BODY COMPRISING A COVER MEMBER OF ELECTRICAL INSULATING MATERIAL ATTACHED TO SAID BODY, UNIFORMLY CIRCUMFERENTIALLY SPACED CONTACT ELEMENTS EXTENDING AXIALLY INTO THE CAVITY AT THE PERIPHERY THEREOF, A BODY OF MERCURY IN THE CAVITY FORMING A POOL THEREIN WHEN THE SWITCH IS NOT ROTATING OF SMALLER CIRCUMFERENTIAL EXTENT THAN THE DISTANCE BETWEEN ADJACENT ONES OF SAID CONTACT ELEMENTS AND FORMING AN ANNULAR LAYER ABOUT THE PERIPHERY OF SAID CAVITY WHEN THE SWITCH IS ROTATING ON SAID AXIS, SAID LAYER ELECTRICALLY INTERCONNECTING SAID ELEMENTS, FIRST AND SECOND ELECTRICALLY CONDUCTIVE RING MEMBERS CONCENTRIC WITH SAID AXIS CARRIED BY SAID BODY AND INSULATED FROM EACH OTHER, ALTERNATE OF SAID CONTACT ELEMENTS BEING CONNECTED WITH DIFFERENT ONES OF SAID RING MEMBERS, SAID CONTACT ELEMENTS BEING PRINTED IN SAID CAVITY, AND MEANS CARRIED BY THE SWITCH ENTIRELY OUTSIDE SAID CAVITY FOR CONNECTING THE SWITCH TO THE END OF A ROTARY MEMBER. 